The Spatial and Temporal Distribution of Insulin-Like Growth Factor-1 Following Experimental Myocardial Infarction in the Rat

Insulin-like growth factor-1 (IGF-1) is believed to be involved in the repair and adaptation that follow ischemic injury to the myocardium. The aim of this study was to elucidate the role of IGF-1 by defining the changes that occur in its distribution following regional myocardial infarction. The left anterior descending coronary artery was ligated in adult male Wistar rats, and hearts were examined microscopically from 6 hours to 20 days later. IGF-1 was identified histochemically using the avitin-biotin-peroxidase method with a polyclonal antibody to IGF-1 and was quantified by optical density measurements of standard fields in sections of hearts prepared in a single batch. Immunoreactivity was located in the cytoplasm of viable myocytes, vascular smooth-muscle cells, mast cells, leukocytes, endothelial cells, and fibroblasts. The zone of viable myocardium immediately adjacent to infarcts reacted significantly more intensely for IGF-1 than all other regions at all stages, with a maximum optical density (617% higher than sham-operated control myocardium, p < .001) 24 hours after coronary artery ligation. Immunoreactivity in myocardium tissue distant from the infarcts also increased during the first day (382% at 24 hours), but this increase was not statistically significant thereafter. These temporal and spatial changes in the distribution and amount of IGF-1 indicate that this finding is predominantly associated with a localized response to injury by the viable myocytes adjacent to infarcts.